Separation methods for water treatment include a method using heat or phase-change, a method using a filtering membrane, and so on. Among the advantages of the method using a filtering membrane is the high reliability of water treatment since the water of desired purity can be easily and stably obtained by adjusting the pore size of the filtering membrane. Furthermore, since the method using a filtering membrane does not require a heating process, it can be used together with microorganisms which are useful for separation process but vulnerable to heat.
Among the methods using a filtering membrane is a method using a hollow fiber membrane module comprising a bundle of hollow fiber membranes. Typically, a hollow fiber membrane module has been widely used in the field of microfiltration for obtaining axenic water, drinking water, super pure water, and so on. Recently, the application of the hollow fiber membrane module is being extended to wastewater treatment, solid-liquid separation in a septic tank, removal of suspended solid (SS) from industrial wastewater, filtration of river, filtration of industrial water, filtration of swimming pool water, and the like.
The hollow fiber membrane module may be classified into a submerged-type module and a pressurized-type module in accordance with the driving method.
The submerged-type module performs the filtration operation while submerged in a water to be treated. Particularly, as the negative pressure is applied to the inside of the hollow fiber membrane, only the fluid component is allowed to pass through the hollow fiber membrane and enter the inside (lumen) thereof. As a result, the pollutants such as the impurities and sludge contained in the water are separated from the filtrate. The submerged-type module is advantageous in that it does not require additional facilities for circulating the water, and thus the cost of equipment itself as well as the operation cost can be reduced. On the other hand, it has a drawback in that the permeate flux obtainable per a unit time is limited.
On the contrary, although requiring additional facilities for circulating the water, the pressurized-type module pressurizing the water from the outside to the inside of the hollow fiber membrane is advantageous in that its permeate flux obtainable per a unit time is greater than that of the submerged-type module.
As illustrated respectively in the Korean patent application laid-open publication Nos. 10-2012-0122381 and 10-2012-0140329 filed by the present applicant, in a conventional pressurized-type hollow fiber membrane module, both ends of a hollow fiber membrane disposed inside a case are potted in different fixing parts respectively. In other words, since the body portion of the hollow fiber membrane performing a filtration process is positioned between the two fixing parts in the case, when the hollow fiber membrane is damaged, it is impossible to repair it, and thus the entire module should be discarded.
In order to increase the treatment capacity of the filtration apparatus, it may be considered to increase both lengths of the case and hollow fiber membrane therein. The longer the length of the hollow fiber membrane is, however, the greater the frictional force which prevents the filtrate flow along the lumen of the hollow fiber membrane is, thereby decreasing the permeate flux of the hollow fiber membrane.
As another method to increase the treatment capacity of the filtration apparatus without increasing the length of the hollow fiber membrane, it may be considered to connect a plurality of pressurized-type modules in parallel. Such method, however, requires more complicated water-circulating facilities, and thus makes it more difficult to install a filtration apparatus. Furthermore, it also requires the increase of footprint of the filtration apparatus.